1. Field of the Invention
This invention relates to a vehicle safety running control system, more particularly to a vehicle safety running control system which detects an obstacle present ahead of the vehicle to determine whether the vehicle may come in contact with the obstacle and operates the braking system, if necessary.
2. Description of the Related Art
Various obstacle avoidance techniques have hitherto been proposed. For example, Japanese Laid-open Patent Application Hei 6(1994)-298022 teaches detecting the distance (relative distance) to an obstacle (e.g., another vehicle running ahead on the road) from the vehicle and automatically operating (i.e., independently of the vehicle operator's brake pedal manipulation) the braking system (and an alarm) so as to avoid contact with the obstacle.
In this prior art technique, the acceleration of the other vehicle (obstacle) is detected and, based on the detected acceleration, a first threshold value (relative distance) for avoiding the obstacle by braking is determined. At the same time, a second threshold value (relative distance) for avoiding the obstacle by steering is determined based on the assumption that the subject vehicle moves to avoid the another vehicle with a lateral acceleration b0 after time .tau., measured from a certain point.
The system operates the braking system automatically only when the detected relative distance falls below the first and the second threshold values. Since the braking system is not operated at unexpected times which are not anticipated by the vehicle operator, the operator does not experience annoyance caused by the automatic braking when he is intending to steer to avoid an obstacle, thereby improving the driving comfort and preventing annoyance of the vehicle operator.
The first threshold value for obstacle avoidance by braking is not always shorter than the second threshold value for that by steering. The relationship therebetween depends on the relative distance.
In the prior art system, however, even when the first threshold value is shorter than the second threshold value, the automatic braking is only effected if the relative distance drops below the first and second threshold values, more precisely, below the first threshold value. As a result, the automatic braking may sometimes be late, needing a large braking force (sudden braking) to be generated.
In such a case, it will be better to initiate the automatic braking earlier whenever it is found that the obstacle avoidance by steering is impossible, since this will not create a problem of interference with the operator's steering and will make it possible to conduct the obstacle avoidance more securely and more effectively. Moreover, this earlier automatic braking will match the intentions of the vehicle operator.
Furthermore, when the relative speed is small, the relative distance to initiate obstacle avoidance control, more specifically the threshold value (relative distance) for obstacle avoidance by automatic braking will usually be small. As a result, the control accuracy may sometimes be degraded depending on the performance of an obstacle detector such as a laser radar or a millimeter-wave radar (e.g., the scanning area, scanning accuracy and resolving power of the radar).